U.S. patent application number 10/065501 was filed with the patent office on 2003-05-29 for fully automatic and energy-efficient deionizer.
Invention is credited to Chiu, Ming-Liang, Chung, Hsing-Chen, Hsieh, Fei-Chen, Hsieh, Yu-His, Lai, Ying-Jen, Shiue, Lih-Ren, Sun, Abel.
Application Number | 20030098266 10/065501 |
Document ID | / |
Family ID | 46204624 |
Filed Date | 2003-05-29 |
United States Patent
Application |
20030098266 |
Kind Code |
A1 |
Shiue, Lih-Ren ; et
al. |
May 29, 2003 |
Fully automatic and energy-efficient deionizer
Abstract
A fully automatic deionizer comprising five sub-systems for
removing ionic contaminants from various liquids at low energy
consumption is devised. Based on the charging-discharging principle
of capacitors, the deionizer conducts deionization through applying
a low DC voltage to its electrodes for adsorbing ions, while more
than 30% of the process energy is recovered and stored by
discharging the electrodes. At the mean time of discharge, surface
of the electrodes is regenerated on site and reset for performing
many more cycles of deionization-regeneration till the desirable
purification is attained. In one moment, both deionization and
regeneration proceed simultaneously on different groups of
electrode modules, and in the next moment the electrode modules
quickly switch the two processes. Such swift reciprocating actions
are engaged in synchronized coordination of sub-systems of
electrode modules, energy management, fluid flow, and automatic
control.
Inventors: |
Shiue, Lih-Ren; (Hsinchu,
TW) ; Sun, Abel; (Taipei, TW) ; Chung,
Hsing-Chen; (Hsinchu, TW) ; Hsieh, Fei-Chen;
(Taichung, TW) ; Hsieh, Yu-His; (Changhua, TW)
; Chiu, Ming-Liang; (Changhua, TW) ; Lai,
Ying-Jen; (Chunghua, TW) |
Correspondence
Address: |
JIANQ CHYUN INTELLECTUAL PROPERTY OFFICE
7 FLOOR-1, NO. 100
ROOSEVELT ROAD, SECTION 2
TAIPEI
100
TW
|
Family ID: |
46204624 |
Appl. No.: |
10/065501 |
Filed: |
October 25, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10065501 |
Oct 25, 2002 |
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09948852 |
Sep 7, 2001 |
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6462935 |
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10065501 |
Oct 25, 2002 |
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10109825 |
Mar 27, 2002 |
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Current U.S.
Class: |
210/87 ;
204/228.3; 210/143; 210/243; 210/97 |
Current CPC
Class: |
Y02E 60/13 20130101;
B82Y 30/00 20130101; C02F 2201/4615 20130101; C02F 2001/46133
20130101; H02J 1/14 20130101; C02F 2201/46125 20130101; C02F
1/46104 20130101; C02F 2001/46152 20130101; H01G 11/08 20130101;
C02F 2201/4611 20130101; C02F 2001/46157 20130101; C02F 2201/46165
20130101; C02F 2201/4617 20130101; C02F 2209/006 20130101; C02F
2303/16 20130101; C02F 1/4691 20130101; C02F 2103/08 20130101; C02F
2001/46138 20130101; C02F 2101/20 20130101; C02F 2209/005 20130101;
C02F 2201/46145 20130101 |
Class at
Publication: |
210/87 ; 210/97;
210/143; 210/243; 204/228.3 |
International
Class: |
B01D 017/12 |
Claims
1. A fully automatic deionizer, comprising: at least one treating
unit, comprising an electrode module and a housing, wherein the
electrode module comprises at least one pair of anode and cathode
made by coating an active material on an electrically conductive
substrate; at least one DC power source to supply electricity to
the electrode module for removing ionic species from liquids, i.e.,
for deionization; at least one capacitor to store electricity
extracted from the electrode module for desorbing the ionic species
from the electrode module, i.e., for regenerating the electrode
module; at least one on-line sensor and at least one fluid valve
for detecting and for diverting liquid flow in the treating unit;
and at least one micro-controller for controlling the deionization,
the electricity extraction from the electrode module, and the
liquid flow.
2. The fully automatic deionizer of claim 1, wherein the active
material is selected from a group consisting of activated carbon,
C.sub.60, carbon nanotube, MnO.sub.2, Fe.sub.3O.sub.4 and
combination thereof.
3. The fully automatic deionizer of claim 1, wherein the
electrically conductive substrate is selected from a group
consisting of Ti, Pt and Pd.
4. The fully automatic deionizer of claim 1, wherein the
electrically conductive substrate is in the form of foil, plate,
mesh, or web.
5. The fully automatic deionizer of claim 1, wherein the electrode
module is in the form of cylinder, cube, or rectangle.
6. The fully automatic deionizer of claim 1, wherein the DC power
source applies a DC voltage to the electrode module for a period
from 30 seconds to 4 minutes for deionization.
7. The fully automatic deionizer of claim 6, wherein more than 30%
of a process energy of the deionization is recovered from the
electrode module.
8. The fully automatic deionizer of claim 1, which is designed so
that electricity is extracted from the electrode module in less
than one minute.
9. The fully automatic deionizer of claim 1, wherein a liquid is
provided to transport the ionic species desorbed from the electrode
module to a reservoir.
10. The fully automatic deionizer of claim 9, wherein the ionic
species are stored in the reservoir to be concentrated for recycle,
for recovery, or for disposal.
11. The fully automatic deionizer of claim 9, wherein the liquid is
selected from a group consisting of fresh water, brine and
seawater.
12. The fully automatic deionizer of claim 1, wherein the capacitor
is selected from a group consisting of supercapacitor,
ultracapacitor and electric double layer capacitor.
13. The fully automatic deionizer of claim 1, wherein the on-line
sensor is used to on-line monitor conductivity, resistivity, pH,
temperature, or optical absorbance of liquids.
14. The fully automatic deionizer of claim 1, wherein the fluid
valve is actuated and controlled by electrical current.
15. The fully automatic deionizer of claim 1, comprising a
plurality of treating units connected in series, a plurality of
on-line sensors and a plurality of fluid valves, wherein at least
one on-line sensor and at least one fluid valve are used for
detecting and for diverting liquid flow in one treating unit.
16. A fully automatic deionizer, comprising: at least two sets of
treating units, wherein each set comprises at least one treating
unit that comprises an electrode module and a housing, wherein the
electrode module comprises at least one pair of anode and cathode
made by coating an active material on an electrically conductive
substrate; at least one DC power source to supply electricity to
the electrode modules for removing ionic species from liquids,
i.e., for deionization; at least one capacitor to store electricity
extracted from the electrode modules for desorbing the ionic
species from the electrode modules, i.e., for regenerating the
electrode modules; a plurality of on-line sensors and a plurality
of fluid valves, wherein at least one on-line sensor and at least
one fluid valve are used for detecting and for diverting liquid
flow in one treating unit; and at least one micro-controller for
controlling the deionization, the electricity extraction from the
electrode modules, and the liquid flow, wherein a first set of
treating units are switched to deionization and a second set to
regeneration at one moment, while the first set of treating units
are switched to regeneration and the second set to deionization at
next moment.
17. The fully automatic deionizer of claim 16, wherein the active
material is selected from a group consisting of activated carbon,
C.sub.60, carbon nanotube, MnO.sub.2, Fe.sub.3O.sub.4 and
combination thereof.
18. The fully automatic deionizer of claim 16, wherein the
electrically conductive substrate is selected from a group
consisting of Ti, Pt and Pd.
19. The fully automatic deionizer of claim 16, wherein the
electrically conductive substrate is in the form of foil, plate,
mesh, or web.
20. The fully automatic deionizer of claim 16, wherein the
electrode module is in the form of cylinder, cube, or
rectangle.
21. The fully automatic deionizer of claim 16, wherein the DC power
source applies a DC voltage to the electrode module for a period
from 30 seconds to 4 minutes for the deionization.
22. The fully automatic deionizer of claim 21, wherein more than
30% of a process energy of the deionization is recovered from the
electrode modules.
23. The fully automatic deionizer of claim 16, which is designed so
that electricity is extracted from the electrode modules in less
than one minute.
24. The fully automatic deionizer of claim 16, wherein a liquid is
provided to transport the ionic species desorbed from the electrode
modules to a reservoir.
25. The fully automatic deionizer of claim 24, wherein the ionic
species are stored in the reservoir to be concentrated for recycle,
for recovery, or for disposal.
26. The fully automatic deionizer of claim 24, wherein the liquid
is selected from a group consisting of fresh water, brine and
seawater.
27. The fully automatic deionizer of claim 16, wherein the
capacitor is selected from a group consisting of supercapacitor,
ultracapacitor and electric double layer capacitor.
28. The fully automatic deionizer of claim 16, wherein the on-line
sensors are used to on-line monitor conductivity, resistivity, pH,
temperature, or optical absorbance of liquids.
29. The fully automatic deionizer of claim 16, wherein the fluid
valves are actuated and controlled by electrical current.
30. The fully automatic deionizer of claim 16, wherein each set of
treating units comprises a plurality of treating units that are
connected in series, a plurality of on-line sensors and a plurality
of fluid valves.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/948,852, filed Jul. 9, 2001 and entitled
"Replaceable Flow-Through Capacitors for Removing Charged Species
from Liquids". The present application is also a
continuation-in-part of U.S. patent application Ser. No.
10/109,825, filed Mar. 27, 2002 and entitled "Deionizers with
Energy Recovery". Both prior applications are incorporated herein
by reference.
BACKGROUND OF INVENTION
[0002] 1. Field of Invention
[0003] This invention relates to an energy management and other
automatic control systems employed in a deionizer system that can
remove charged species from liquids automatically and continuously
with recovery of the process energy. More specifically, this
invention relates to ion removal systems using capacitive
deionization (CDI) on a number of flow-through capacitors (FTCs) in
conjunction with supercapacitors, ultracapacitors, or electric
double layer capacitors as the energy-storage device for storing
the electrical energy that is reclaimed during the regeneration of
FTCs.
[0004] 2. Description of Related Art
[0005] There are numerous pollutants of inorganic, organic, or
biological nature in the contaminated liquids and waters. Many
methodologies and techniques can be used to decontaminate the
impure fluids, nevertheless, none of the methods is universal.
Among the pollutants, charged species or ions are probably the most
frequently occurring source of contamination. This is due to that
the contaminants often dissolve as ions, or they are dissociated or
hydrolyzed into ions in the liquids. In either case, the
contaminants are described as total dissolved solids (TDS) measured
in ppm (parts per million). It requires a special treatment other
than a simple filtration to reduce the TDS to acceptable levels for
use or discharge. No matter what method is adopted, it should
fulfill the following requirements: 1) low cost, 2) high
efficiency, 3) no secondary pollution, 4) robust, and 5) energy
efficient, for a method to become a cutting-edge technique on
purifying liquids.
[0006] Ion-exchange and reverse osmosis (RO) are presently two
popular techniques utilized for the reduction of TDS. Before
applications, ion-exchange resins must be pre-conditioned in
chemicals such as strong acids or bases followed by rinsing with
copious de-ionized water. Strong chemicals and high-quality water
are also used to regenerate the resins. Regeneration of
ion-exchange resins can only be repeated in a limited number of
cycles as the resins are vulnerable to degradations. Therefore,
ion-exchange method is wasteful in terms of consuming chemicals and
water, and the process generates secondary pollutions during
precondition and regeneration of the resins. Opposite to the
natural migration of solvent in osmosis, pure solvent is
transferred from the high concentration side to the dilute side
through fine pores of RO membranes in RO operation. To counteract
the osmotic pressure, which is existent in all solutions and
increases with the concentration of solutions, RO requires the
application of pressures on the RO membranes for extracting the
pure solvent from solutions. Therefore, the process energy of RO is
high, which is also aggravated by most liquid is not recovered, and
pollutants are left behind making the original liquids more
polluted. As the pores of RO membranes are so fine, for example,
0.5 .mu.m, that they are prone to fouling, as a consequence, they
rely on costly pre-treating setups for protection. Regeneration of
the RO membranes is also wasteful by consuming chemicals and pure
solvents without mentioning the generation of secondary
pollution.
[0007] Since TDS is associated with charged species,
electro-technology, especially capacitive deionization (CDI) is a
more sensible method than ion exchange and RO on reducing the ionic
wastes. CDI utilizes the configuration of capacitor, or a
flow-through capacitor (FTC) to be specific, wherein an
electrostatic field is built with the application of low DC
voltages to the electrodes for adsorbing ions as the ion-containing
liquids flow through the electric field. Electricity is used to
modulate the removal of ions, or purification of liquids,
containing many adjustable parameters that impart CDI considerable
maneuver-abilities.
[0008] There are many CDI and FTC works granted in the US patent
publications, some typical examples can be found in U.S. Pat. Nos.
3,515,664, 3,658,674, 5,425,858, 5,514,269, 5,766,442, 6,022,436,
6,325,907, 6,346,187, 6,410,428, and 6,413,409. They are all
incorporated herein by reference. Though various fabrication
methods of electrodes and electrode modules, as well as
miscellaneous patterns of liquid-flow, are disclosed in the prior
art, they are generally lack of an implementing methodology to
become commercially viable on treating massive liquids. One of the
miscomprehended arrangements of conducting CDI in the prior art is
that the fundamental properties of capacitors, for example, fast
charging and fast discharging, are overlooked. In essence, the
adsorption of ions on the electrodes of CDI module is the same
process as the charging of capacitors, while desorption of ions
from the CDI electrodes is equivalent to the discharging of
capacitors. As the charging and discharging of capacitor normally
take place in a matter of seconds, as well as repeat in numerous
cycles, the ion-adsorption and ion-desorption of CDI technique
should be conducted swiftly without unduly delay. Furthermore,
energy is harvested at capacitor discharging because that is the
reason that energy is invested at charging. Thence, energy can be
reclaimed as a by-product at the regeneration of the CDI
electrodes. Unlike ion-exchange and RO, no chemicals and pure
solvents are consumed, nor secondary pollution is generated during
the regeneration of CDI electrodes. It is due to that low process
energy is used for deionization, energy is recovered at
regeneration, and the foregoing processes are rapidly completed
that transforms the CDI technique into a method of low cost and
high productivity for environmental applications.
SUMMARY OF INVENTION
[0009] The present invention provides an implementing method of
automatic CDI for commercially producing fresh water via
desalination or recycling waste waters, for liquid waste reduction,
and for other high value-added applications.
[0010] Both ion adsorption on the electrodes of CDI modules and
regeneration of the CDI electrodes are fundamental physical
processes in the nature. While the surface adsorption is due to
electrostatic attraction, the electrode regeneration occurs by
means of static-charge dissipation, just like the charging and
discharging of capacitors, the two processes of CDI will respond
promptly and reversibly to the external actuations. It is the
intent of the present invention to devise a fully automatic system
utilizing the foregoing physical processes for producing fresh
water, pure solvents, and useful resources with a high
energy-efficiency. In accordance with the present invention, one
object is to use an economical material as the active adsorbent of
ions. First of all, the material should be adsorptive, conductive
and inert in adverse conditions such as strong acids, strong bases,
strong oxidants, and organic solvents. Among many choices,
activated carbons (ACs) are one ideal group for CDI applications.
Unless added benefits to justify the extra efforts put on preparing
extraordinary carbonaceous materials, otherwise, an inexpensive and
commercially available AC is good enough for some CDI applications.
Using conventional means, for example, roller coating, and with the
assistance of a binder, powder of an ordinary activated carbon can
be attached to a metallic support forming the electrodes of
CDI.
[0011] Another object of the invention is to construct the
electrode modules of CDI in a simple and effective assembly. All
modules should allow free path to liquids as in regular FTCs. In
order to attain high adsorption efficiency, all of the impure
liquid must be subjected to the static electric field built within
the electrode modules. This means that the fluid must pass between
the charged electrodes and there is no bypath for the un-treated
liquid to escape, as well as no concealment in the container of FTC
for the liquid to remain un-treated. Thus, simple assemblies as
normally used for capacitors, for example, spiral winding and
parallel stacking, are adopted to make FTCs to fit into the
housings of desirable shapes and dimensions in a liquid-treating
system. To fit the shapes of various housings, the electrode module
can be in the form of cylinder, cube, or rectangle. Hermetic
sealing and flow guides are provided in the treating units
comprised of FTCs and housings to ensure the requisite pattern of
liquid flow.
[0012] Following the completion of CDI treating units, there should
have an energy manager to govern the reciprocating deionization and
regeneration, or charging and discharging, of the electrode modules
for purifying liquids. It is yet another object of the invention to
devise an energy management sub-system comprising of a DC power
source, an energy-storage device, and a micro-controller that
allows the settings of various durations for conducting either
deionization or regeneration as desired. Electricity is supplied to
the electrodes from the power source for deionization, whereas the
residual energy of the electrodes is released to the storage device
during regeneration. Both processes should be modulated to continue
for appropriate durations without unduly delay. Also, the DC
voltage is controlled at a level only to sustain an electric field
for electrostatic attraction of ions, rather than causing
electrochemical reactions.
[0013] Yet another object of the invention is to devise an
automation sub-system comprising of a micro-controller, on-line
sensors and electromagnetic fluid values. As the sensors detect the
purity of effluent of a particular CDI treating unit below a
predetermined level indicating the requirement of regeneration,
upon a signal from the sensors, the controller will divert the
flow-direction of electromagnetic valves so that the influent can
be changed from liquid to be treated to the regeneration liquid. At
the meantime, the electrode module will automatically be converted
from deionization to regeneration, or from charging to discharging.
All of the on-line monitoring, liquid-flow diversion, and energy
transfer can be programmed to set up a desirable sequence of
events, and as many cycling times of treatments as necessary
without human attention.
[0014] Still another object of the invention is to devise a fully
automatic CDI setup as a pre-treatment for the more expensive and
fragile liquid-treating equipment such as ion-exchange and RO. CDI
is capable of directly purifying high-concentration liquids such as
seawater, so the TDS of liquids can be reduced to the suitable
levels for ion exchange and RO that the service life of the latter
can be prolonged. Because of the low cost of materials used,
energy-efficiency of operation and pollution-free characteristics,
the fully automatic CDI system of the invention can offer cross
cutting benefits to the waste reduction of various liquids.
[0015] A further object of the invention is to devise a fully
automatic CDI setup to recycle useful resources for reuse. During
the regeneration of CDI electrode modules, a rinsing liquid is
employed to transfer the desorbed ions, the ionic contaminants that
are removed from the liquids at deionization, to a designated
reservoir wherein useful resources can be concentrated and
recovered. Not only the sludge from the purification treatment is
easy for disposal, the present invention also provides values added
to the reduction of liquid wastes by recycling useful resources for
reuse in an economical fashion.
[0016] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF DRAWINGS
[0017] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention. In the
drawings,
[0018] FIG. 1A is an illustration showing ions of a brine solution
are adsorbed by a pair of coated plates, charged by a DC power
source, as the fluid flowing through the plates in a preferred
embodiment of the invention. The accumulation of charges on the
plates is equivalent to the charging of an electrochemical
capacitor;
[0019] FIG. 1B is an illustration showing as the ion-covered plates
are connected to a load, the ions are desorbed in correspondence to
the discharging of electricity to the load in the preferred
embodiment of the invention. Desorption of ions, which is
equivalent to the discharging of an electrochemical capacitor,
regenerates the surface of plates;
[0020] FIG. 2 is the principal scheme of a continuous flow and
fully automatic CDI setup containing a tandem separator of three
CDI treating units in the preferred embodiment of the
invention;
[0021] FIG. 3 is a flow chart of the operating logic of a fully
automatic CDI system in the preferred embodiment of the invention,
wherein seawater is used as an example; and
[0022] FIG. 4 is a plot showing the reduction of TDS and the change
of salt rejection rate of a seawater sample subjected to a
four-minute deionization in a CDI treating unit in the preferred
embodiment of the invention.
DETAILED DESCRIPTION
[0023] Capacitor is deeply involved in human life from the
integrated circuits that create the digital era, to the planet
wherein human lives, for the earth is in essence a large spherical
capacitor. In nature, charges are generated and cumulated in clouds
from collisions between heavier ice pellets and lighter ice
crystals, and the charges may be discharged in a fraction of a
second which is often seen as lighting. Man-made capacitors are
also capable of charging and discharging in less than a second.
There are two kinds of capacitors, namely, electrostatic capacitor
and electrochemical capacitor. An inorganic or organic electrolyte
comprising a solvent and a soluble and dissociable salt is enclosed
in the electrochemical capacitors to impart the capacitors high
capacitance. When each of the two conducting plates of the
electrochemical capacitor is connected to one terminal of a DC
power source, it will instantly attain the same polarity and
potential of that terminal. At the same time, the positively
charged plate can attract the anions of the electrolyte, while the
negative terminal of the capacitor attracts the cations. It is the
adsorption of positive and negative ions, that is, cations and
anions, on the surface of the capacitor plates or electrodes that
constitutes the capacitance of the electrochemical capacitors. The
process of charge accumulation through the application of a DC
voltage to the plates of capacitors is the charging of capacitors.
Depending on the values of capacitance and internal resistance of
the capacitors, the charging times of capacitors may range from a
fraction of a second to several seconds. FIG. 1A shows one
preferred embodiment of the invention using two parallel plates
coated with an adsorbent, indicated by the rough terrain, as two
electrodes to form a capacitor. For the sake of clearance, no
numerical number is assigned to the components in FIG. 1A, nor
number is given to those in the following FIG. 1B. As shown in FIG.
1A, when the two conducting plates are connected to a DC power
source represented by the symbol of battery, every up-and down tip
of the rough terrain on the plates will instantly attain the same
polarity but lower potential of that charged plate. In other words,
there are numerous electro-statically attracting centers on each of
the positively and negatively charged plates for adsorbing ions. As
soon as a brine solution flows through the charged plates, the
cations will be attracted by the negatively charged centers and the
anions will be drown to the positive sites. Whereas the foregoing
adsorption of ions on the surface of electrodes is the charging
process of capacitor, the same process of FIG. 1A is deionization
of the brine, as a result, the brine may become fresh water.
Removal of ionic species from liquids by a method as FIG. 1A is
named capacitive deionization (CDI).
[0024] It is known to people skilled in the art that the conducting
plate employed in CDI is called substrate or current collector,
while the adsorbent is active material. The substrate can be in the
form of foil, plate, mesh, or web. Deionization or desalt is the
principal goal of CDI, the technique only requires a low DC
voltage, for example, 0.5-3V, so that electrolysis is inhibited.
Furthermore, both current collectors and active material should be
adsorptive, conductive, and inert in various harsh environments. If
CDI is employed for desalination, titanium (Ti) is the best choice
for the current collector in terms of resistance to salt corrosion
and material cost. Nevertheless, platinum (Pt) and palladium (Pd)
can be used as the substrate for the stringent applications such as
hemodialysis. Because of their absorption capability, large
specific surface area, and low cost, activated carbons (ACs) are
the most convenient choice for the active material of CDI. There
are numerous ACs available on the market that makes the selection
of material laborious. In addition to cost, the chosen AC should
have minimum surface area of 1000 m.sup.2/g, minimum size of 200
mesh, and 0% ash content. Other costly carbonaceous materials such
as the Bucky ball, C.sub.60 and carbon nanotube can also be used at
low loading. For mild and neutral liquids, metal oxides such as
manganese oxide (MnO.sub.2) and magnetite (Fe.sub.3O.sub.4) having
specific adsorption so that the use of them is beneficial to
special CDI applications. As the charging rate of capacitors is
fast, CDI operations ought to be short for the surface of
electrodes is quickly saturated with ion coverage. Under low
operating voltage and short operating time, CDI is highly
energy-efficient on reducing the TDS of liquids. It is estimated
that CDI requires the consumption of energy no more than 1 KW/hr to
desalinize 1 tonne (263 gallons) of 35,000 ppm seawater to 250 ppm
fresh water. After treatment, the degree of purity of the fresh
water in FIG. 1A is determined by the adsorption capability, and
the effective surface area of the active material, as well as by
the gap between the CDI electrodes.
[0025] When the electrodes of FIG. 1A become saturated, they need
regeneration, or desorption of ions, to resume adsorption
capability. Just like the discharging of electrochemical capacitors
leading to the returning of ions to the electrolyte, the saturated
CDI electrodes can free their surface from ions by discharging to a
load as shown in FIG. 1B. Three key features of the regeneration of
CDI electrodes must be comprehended for the technique to be
commercially viable in environmental applications and desalination.
Firstly, regeneration of CDI electrodes can be and should be
conducted as swiftly as the discharge of capacitors. Secondly, with
discharge the adsorbed ions will automatically leave the CDI
electrodes. Thus, any solution can be employed to transport the
desorbed ions to a designated reservoir wherefrom useful resources
can be concentrated and recovered. Only a small amount of rinse, as
seen in FIG. 1B, in high purity is needed to clean the electrodes
to minimize cross-contamination. Thirdly, the residual energy of
the saturated CDI electrodes must be recovered and stored in a
device for future use. It is estimated that more than 30% of the
process energy applied during deionization can be recovered at
regeneration.
[0026] The amount of energy available for recovery is often
enormous and profitable. For example, a desalination plant of daily
production of 30,000 tonnes (ca. 7,900,000 gallons) fresh water
using CDI technology, will require 30,000 KWh of energy for
deionization process, and there is 9000 KWh of the process energy
can be reclaimed. To recover such huge energy immediately,
supercapacitor, also known as ultracapacitor and electric double
layer capacitor, is a far more effective energy-storage device than
battery, inductor, or flywheel to do the job. This is because
supercapacitors have high volumetric energy densities and they can
be charged at electronic speed, accepting any magnitude of charging
currents without generating heat or hysteresis. Based on a per unit
size and weight basis, capacitive energy transfer is far more
effective than the inductive energy transfer is. Spirally winding
or closely stacking is generally used to manufacture capacitors.
Some physical means are disposed between the electrodes to
electrically isolate the electrodes. The CDI electrodes can adopt
the same assembly fashion of conventional capacitors to form
various modules to mate the desired housings in the liquid-treating
systems. A CDI treating unit is thus constituted by the electrode
module and its housing. Not only liquid leak is prevented in the
unit, but also all the impure or un-treated liquid must flow
through the electrostatic field built within the electrode module,
and the impure liquid is prohibited from mixing with the treated
liquid. Since CDI is operated under the ambient condition, the
piping and connection for the desired fluid flows can be set up
easily and maintained economically. However, energy recovery at the
regeneration of CDI modules must be prompt and complete,
cross-contamination form liquids must be low, and the layers of
active material must remain effective for a long period of time,
only then the operation cost of CDI can be as low as its material
cost as depicted in the present invention.
[0027] One preferred embodiment of a fully automatic CDI system
containing a tandem separator of three CDI treating units connected
in series, designated as 200, is shown in FIG. 2. Only the major
portions of the system are displayed in the drawing, and some
detailed parts, as will be specified below, are omitted for
clearance. There are five sub-systems to form a complete automatic
CDI system, namely, 1) the electrode sub-system as indicated by E1,
E2, and E3, 2) the CDI-treating-unit sub-system designated by C1,
C2 and C3, 3) the energy-management sub-system constituted by
micro-controller (.mu. C), DC power source and supercapacitor
(S/C), 4) the fluid-flow sub-system of fluid flow-pipes and
connectors, and 5) the automatic control sub-system consisting of
the micro-controller (.mu. C), on-line sensors (S1, S2 and S3), and
electromagnetic fluid-flow valves (T). Though only three CDI
treating units are illustrated in FIG. 2, as many units arranged in
any combination, in series or in parallel or combination thereof,
can be disposed to form a CDI liquid-treating system as desired.
Also, FIG. 2 is so simply constructed that the CDI electrode
modules E1, E2, and E3 are shown in cylindrical shape, and their
housings C1, C2 and C3 are of rectangle, while the electrode
modules and the housings are not snuggly assembled. All of the
foregoing is depicted for the sake of clearance.
[0028] In the operation of automatic CDI 200, an impure liquid such
as seawater can be conveyed by pump 202 from tank 201 through
electromagnetic fluid valve 203, 204 or 205 to the CDI treating
unit C1, C2, or C3, respectively. As the impure liquid flows into
the treating units, the micro-controller .mu. C will synchronously
direct the DC power source to supply electricity to the electrode
module of that treating unit to perform deionization for a preset
duration. The DC power source applies a DC voltage to the treating
unit for a period from 30 seconds to 4 minutes for deionization. On
the conclusion of a deionization session, the on-line sensors S1,
S2 and S3 measure the conductivity, resistivity, pH, or optical
absorbance of the effluent, in reference to a predetermined
standard, to determine if the effluent is ready for harvest, or it
requires further deionization treatment. If the effluent is pure
according to the judgment, the sensor notifies the microprocessor
.mu. C to divert the electromagnetic flow valve 206, 207 or 208 to
allow the pure liquid flowing through electromagnetic valve 209,
210 or 211, as well as through liquid pipe line 216, 218, or 220,
respectively, to line 222 and into tank 212 to store for later use,
or for transporting to a local water-supply system. There is a
check value arranged on line 222 (not shown in FIG. 2) to prevent
pure liquid back flow from the storage tank 212 back to the CDI
treating unit (C1, C2, or C3). As long as the effluent is pure,
more impure liquid can be conducted into that CDI treating unit
(C1, C2, or C3) for deionization, otherwise, the influent will be
switched from impure liquid (of tank 201) to the rinse supplied
from tank 213 by the pumping of a pump 214. When the rinsing liquid
flows to a CDI treating unit, the impure liquid flow to that unit
will be terminated and all of the electromagnetic valves will be
arranged, on the commands issued by the micro-controller .mu. C,
for the pass of rinsing liquid. Same as deionization, regeneration
of the CDI electrode modules in the presence of rinsing liquid is
also conducted for a pre-set duration, such as a duration less than
one minute. On the conclusion of a regeneration session, the
effluent of rinsing liquid, together with the desorbed ions, flows
through pipe line 215, 217 or 219 into line 221 and back to the
tank 213 wherefrom valuable ions can be concentrated and recycled
for reuse, or collected as by-products for sale enhancing the value
of CDI treatment.
[0029] Deionization of liquid and regeneration of the CDI electrode
modules should be conducted simultaneously on separate groups of
CDI treating units for two reasons. The first reason is that impure
liquids in the industrial scale are frequently copious, the impure
liquids should continuously flow through many parallel sets of CDI
treating groups, each group containing a number of CDI treating
units connected in series, to attain a high throughput. The second
reason is that a tandem CDI treating units can facilitate the
energy recovery at regenerating the electrode modules. More units
connected in series, higher recovery rate and deeper discharge of
each electrode modules can be attained. As the discharge of
capacitors will cease when an equal potential is arrived, the
serially connected capacitors can provide a larger potential range
for discharge, thus a deeper discharge on each capacitor. While
some groups of CDI units are subjected to regeneration, other
groups will be performing deionization. Deionization and
regeneration are quickly repeated and interchangeably among many
groups of tandem CDI treating units. Therefore, fresh water and
electricity are co-generated in the automatic CDI system of the
present invention. In order to cope with the fluid flow rate, which
is considerably slower than the electronic response, deionization
and regeneration of CDI are accordingly set to appropriate
durations of operation. The flow pattern through the whole CDI
treating system can be programmed for any liquid flowing in any
group of CDI treating units for any duration, arranged in any
desired sequence of events.
[0030] To illustrate the operating logic of the invention, one
preferred embodiment of process flow chart 300, using seawater as
influent, is displayed in FIG. 3. After the deionization at CDI#1
of step 301, if the effluent is below 250 ppm at the determination
of step 302, that effluent will be stored in the tank of fresh
water. Otherwise, the effluent is sent to CDI#2 of step 303 for
further deionization. Then, the next effluent is judged at step 304
for harvest, or for further deionization until CDI#n of step 305.
On the other hand, when a CDI electrode module requires
regeneration, a regenerating fluid will be injected from the tank
310, through pipe line RE1, RE2, or REn, to that module to perform
regeneration with energy recovery (not shown in FIG. 3). On the
conclusion of a regeneration session, the regenerating liquid exits
that reset CDI treating unit through pipe line RC1, RC2, or RCn,
into the rinse reservoir 320 wherein a decision is made, based on
the ppm of liquid, for returning the liquid to tank 310 for reuse,
or for transferring the concentrated liquid to a station for
extraction of metal ions, for example, Mg.sup.2+ in seawater, or
for cycling other valuable ions for reuse or for sale.
[0031] To demonstrate the feasibility of the present invention, two
examples are provided in the following.
EXAMPLE 1
[0032] Using Ti foils as current collector and a commercial
activated carbon as active material, a cylindrical electrode module
is constructed as that described in the pending U.S. patent
application Ser. No 09/948,852, filed on Jul. 9, 2001. The
activated carbon employed herein has a specific surface area of
1050 m.sup.2/g, particle size of ca. 300 mesh, and it is sold at
$0.35 per pound. The CDI electrode module prepared has a geometric
area of 1140 cm.sup.2 and it is placed in a standardized pressure
vessel commonly used in commercial and residential water purifier
systems. With 3V DC applied to the two terminals of the module,
seawater of 34,000 ppm is continuously flowed through the cartridge
for deionization at a constant flow rate of 1 l/min. During
4-minute deionization, 4 liters of the water has passed the
electrode module under 3V, whereas the current has been observed to
drop from 6A to 1A. The effluent is collected for 1 minute at
1-minute intervals, that is, four samples per run are attained, and
TDS of the treated waters is measured. Four test runs are conducted
with the electrode module reconditioned through energy recovery for
each new run. The Reductions of TDS with one pass of 34,000 ppm
seawater through the cylindrical CDI electrode module are listed in
TABLE 1.
[0033] [t1]
1TABLE 1 Run # Sample TDS (ppm) Salt Rejection # 1 2 3 4 Ave. (%) I
22,800 16,600 14,800 19,100 18,300 46.2 II 31,100 29,100 27,200
30,500 29,500 13.2 III 32,400 31,100 30,200 31,800 31,400 7.6 IV
32,400 31,800 34,500 32,400 32,800 3.5
[0034] Both TDS (in ppt) and salt rejection rate (%) are plotted
against the collection time in FIG. 4. Since the liquid flow rate
is 1 l/min, the abscissa also represents the volume of effluent in
liter. As seen in the graph, TDS of the effluent rises quickly to
the level of influent, whereas the salt rejection rate falls in
correspondence to the change of TDS. Thus, the CDI electrode module
becomes saturated rather quickly indicating that the deionization
should be conducted in a short duration, most likely, less than 30
sec for a higher use efficiency of electrical energy. For
commercial, industrial and residential applications, the geometric
surface area of the electrode module, as well as the number of CDI
treating units, can be custom-made to fulfill the desirable purity
and productivity. At the application of 3V and 6A for 1 minute, the
TDS of 1 liter un-diluted seawater is reduced by more than 40%.
Electricity reclaimed from the process energy is stored in
supercapacitors, which can drive toy cars for a lengthy time.
Therefore, the speed of deionization, or charging rate, of the
present invention is extremely fast, and the energy consumption is
highly economical. Example 1 also indicates that the deionizer of
the present invention can directly purify the un-diluted seawater
without using any pre-treatment equipment, while the electrode
modules can be reconditioned and reused repeatedly without damage
and without adding chemicals, consuming energy, or generating
secondary pollution. Furthermore, the deionizer of the invention
can serve as a pre-treating equipment for concentration-sensitive,
expensive and vulnerable ion-exchange and RO. While most charged
contaminants are removed by the CDI treating units, trace ionic
impurity is easy to be completely eliminated by ion-exchange or
RO.
EXAMPLE 2
[0035] The same CDI treating system and operating voltage as
EXAMPLE 1 is used for purifying an aqueous solution of CuSO.sub.4
containing 2000 ppm Cu.sup.2+. During 3-minute deionization, four
samples of the effluent are collected for half minute at 30 seconds
interval for the first minute, and 1 minute collection at 1 minute
interval for the rest. TABLE 2 lists the TDS of treated
solution.
[0036] [t2]
2 # TDS (ppm) Rejection (%) 1 1820 9 2 1930 3.5 3 1920 4 4 1900
5
[0037] Because Cu.sup.2+ is prone to be reduced at the cathode
resulting in the loss of active surface of the CDI electrode, the
ejection rate in TABLE 2 is considerably lower than that in TABLE
1. for reducible ions, it requires modifications of the active
material and the fluid flow pattern in the electrode module of the
CDI treating systems utilized in the two examples.
[0038] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *